LU79855A1 - NITROGEN-CONTAINING COBALT-CHROME-MOLYBDENE ALLOY - Google Patents

Description

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It is well known in the art of cast alloys based on cobalt containing chromium and molybdenum.

They are characterized by a very advantageous combination of properties at ambient temperature, that is to say the solidity ", 5 the resistance to fatigue" the ductility "the resistance to wear" the resistance to corrosion, the compatibility with biological tissues and moderate hardness and for this reason they have been widely used in dental and orthopedic techniques as raw materials for cast prostheses such as dentures and surgical implants (see, for example, American Society for Testing Materials Designation P 75-67, "Standard Specification for Cast Cobalt-Chromium-Molybdenum Alloy for Surgical Implants"); U.S. Patent Reissued (Reissue) No. Re 15 20,877, U.S. Patent No. 2,674,571) v

U.S. Patent No. 2,180,549 discloses the use of a cobalt-based alloy containing about 10 to 40% chromium, about 5 h 20% molybdenum and up to 0.6% of carbon as raw material for cast articles of prostheses and for wrought metal wires. This alloy has greater resilience, greater toughness and greater resistance to acids than an alloy containing less molybdenum and / or more carbon.

U.S. Patent No. 3,544,315 discloses an alloy for molding dentures consisting essentially of 50 to 60% cobalt, 20 to 28% chromium, 10 to 20% nickel, 3.7 to 4.1% molybdenum and 0.18 to 0.22% carbon. According to this text, the narrow domains of molybdenum and carbon would optimize the combination of strength, hardness, ductility and strength.

The cobalt-chromium-molybdenum cast alloy for surgical implants, sold under the brand name Vitallium (Hovrnedica, Inc., New York, United States) has the following approximate composition: • Percentage by weight Chromium 28

Molybdenum 6

Manganese 0.65 r ". "'n 4 2.

Silicon Ο> 70

Nickel Οι 5

Iron 0.5

Tungsten 0.2 5 Carbon 0.20-0.26 ï

Nitrogen 0.125 - 0.25

Cobalt stays

Nitrogen is added to this cast alloy to improve its tensile properties, resistance to fatigue and ductility at room temperature. Vitallium has world-class properties as a cast alloy for surgical implants and dentistry and has been used widely and successfully for these purposes. However, we are looking for even higher alloy properties, in particular bending fatigue resistance to further improve the performance of this alloy in its critical applications-

It is known that when cobalt alloys are poured into an atmosphere containing nitrogen rather than melting them in a vacuum, these alloys absorb nitrogen in small amounts in their composition [Elsea, AR and HcBride CC, Trans. A.I.M.E.,. 188, 154-161 (1950); Fletcher E.E. and Elsea A.R., Trans. LOVE. 215, 917-925 (1959); Lane J.R. and Grant N.J., Trans. Bitter. Soc. Metals, 44, 113-137 (1952)].

25 More than 20 years ago, it was said that bars made of "stellite 21" (Cabot Corp. Kokomo, Ind.), A cobalt-chromium-molybdenum alloy for surgical implants containing approx. 0.3% carbon and approximately 3% nickel, also contained 0.09 to 0.17% nitrogen (Weeton, J.W. and Signorellî R.A. Trans.

30 Bitter. Soc. Metals 47, 815-852 (1955)).

The manufacture of cobalt-chromium-molybdenum alloy surgical implants has been recommended as workpieces rather than castings to increase strength, ductility, hardness, corrosion resistance, fatigue resistance and to wear. The ductility, the corrosion resistance, the fatigue resistance and the wear resistance of the alloy in the forged state are then improved by a subsequent treatment at approximately 1050 ° C. [Guess T.M., Kummer FCJ. and Wulff J., .1 3.

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Journal of Materials Science * 7, 126-128 (1972); Devine T.M.i Cohen J. and Wulff J. Proceeding3of the New England Conference on Bioengineering (Pope, M.H. et al. Ed.) 136-153 (1973); see also United States patent 5,246,576]

Unfortunately, commercial production of worked surgical implants is economically prohibitive if the final shape of the implant is to be achieved by a method such as cold working with subsequent mechanical adjustment. A clearly preferable route would be to forge the alloy 4 directly into the desired irregular shape. However, no economically feasible method is currently known in which · a commercial alloy for cobalt-chromium-molybdenum surgical implants can be directly forged directly into surgical implants without a high percentage of breakage during forging.

It is known to the technician that it is possible to increase the ductility and the aptitude for cold or hot working of a cobalt-based alloy containing chromium and molybdenum reducing 2o the carbon content of the alloy. Corrosion resistance can also usually be improved by such a reduction (Devine, Cohen and Wulff, cited work). It is generally known that chromium increases strength, hardness and corrosion resistance at the expense of processability, while it is generally known that molybdenum increases strength and hardness at the expense of processability (see United States Patent No. 3,433,631, but also compare United States Patent No. 4,012,229).

The action of small quantities of nitrogen on the processability of the cobalt-chromium-molybdenum alloy and on the properties of the resulting hot worked material is not well understood.

U.S. Patent No. 2,746,860 35 discloses a cobalt-based cast alloy for use at high temperatures containing 23 to 36% chromium, 2 to 15% nickel, 12 to 16% of tungsten, up to 3% molybdenum (the sum of tungsten plus molybdenum not exceeding 16%) j>: · λ 4.

t 0.2 to liΟ% boroni an amount of manganese intended to remove oxygeni up to 5% feri 0.3 to 0.9% carbon and up to 0.25% nitrogen. Hot ductility is seriously impaired when the amount of carbon is greater than 0.4%. Nitrogen is included for high temperature stability towards refrigeration. However, U.S. Patent No. 2,977,244 teaches that a nitrogen content greater than about 0.04% by weight in a cast or worked carbon alloy containing 19 to 22% chromium, 11.5 to * 10 13.5% of tungsten, up to 0.15% by weight of boron, up to 3% of molybdenum and up to 0.25% of carbon is harmful to the stability towards rupture under stress at 927 ° C.

It is taught that the presence of nitrogen, like that of carbon, decreases the cold-processing ability of the cobalt-based fabricated bond described in U.S. Patent No. 3,355,542 (Co — Ni — Cr — Ko) ·

U.S. Patent No. 3,366,478 discloses that the forging ability of an alloy comprising about 15-30% chromium, about 10-30% nickel, about 20-12% tantalum, up to about 3% molybdenum, about 0.03 to 0.20% carbon and the rest of the cobalt increases markedly by the addition of about 0.01 to 5% zirconia. The role assigned to zirconium is to chemically associate with carbon and unwanted elements such as oxygen and nitrogen (which should be kept as low as possible).

The Applicant has discovered a new alloy consisting essentially of approximately 22 to 27% by weight of chromium, approximately 3 to 6% by weight of molybdenum, approximately 0.10 to 0.25% by weight of nitrogen, up to approximately 0.15% by weight of carbon, up to approximately 1% by weight of manganese, up to approximately 1% by weight of silicon, up to approximately 2% of iron, up to approximately 2% of nickel, and the rest in cobalt ", It has a great ability to be hot worked and can be easily forged directly into irregular shapes. Fabricated articles of this alloy have excellent properties of resistance to room temperature, resistance to fatigue, resistance to wear, hardness, ductility, corrosion resistance and excellent compatibility / -Λ 5 .

with biological tissue. This new alloy is thus an excellent raw material for worked surgical implants such as rods extending hip prostheses and surgical nails.

The invention covers this new alloy and worked surgical implants made of this alloy.

It is said that the alloy according to the invention is worked> · as the term is defined here, if it has been hot worked at a temperature above its recrystallization temperature (around 1038 °) at at least once after being cast so as to reduce a linear dimension by at least about 5%. The main purpose of such a treatment is to give solidity and resistance to fatigue to the alloy.

The basic method of preparing the alloy according to the present invention comprises casting an ingot having the desired element content and, if desired, further processing the ingot into a condition of the desired final shape and size alloy. . The alloy can exist in many different conditions depending on its history, for example casting conditions, forging conditions, forging and annealing conditions, forging and recrystallization conditions, cold rolling conditions. The alloy according to the invention can be used as a raw material for molded dentures.

The feed metal charge is melted and poured into ingots by methods well known to the person skilled in the art. Cobalt, chromium and molybdenum are added to the molten metal in the desired proportions in the alloy. The carbon content is adjusted using low carbon feed metal. Small amounts of manganese, silicon, iron and nickel are almost inevitably introduced into the molten alloy as contaminants in the commercially available metal assortment. Manganese and silicon act as deoxidizers during the smelting operation.

Nitrogen can be introduced into the ingot at a reproducible level by any of several methods, for example: i 6.

(a) adding the desired amount of nitrogen to the molten alloy in the form of a body such as CrH and melting in an inert atmosphere (for example argon); (b) melting in a nitrogen atmosphere (nitrogen content, 5 te determined by the partial pressure of nitrogen); and (c) air melting (the nitrogen content is determined by the duration of the melting and the temperature.

Subsequent processing of the ingot may include one or more usual metallurgical operations) such as hot working, homogenization, annealing with dissolution to reduce tensions "a heat treatment for recrystallization of the grains and the increase in ductility (that is to say partial annealing) or cold working according to the desired final properties.

15 A preferred hot work operation is hot forging "roughly defined as working metal at a temperature above its recrystallization temperature" into a shape of defined size using hammers or presses. The alloy according to the present invention can easily be hot-forged without there being a large proportion of breaks directly in solid objects "resistant to fatigue and irregular shapes, for example of rods extending hip prostheses,. at a much lower price than by forming it in irregular shapes by other methods such as cold working followed by mechanical adjustment. Any usual forging method can be used (for example hammer,. stamping, stamping).

The alloy according to the invention forged under the conditions indicated i 30 has at room temperature a tensile strength, a resistance to the elasticity limit, a resistance to fatigue, a hardness a resistance to corrosion by physiological fluids clearly superior to those of the cast alloy of the same composition. A particularly advantageous operation after forging is a partial annealing of an object in the forged state to increase its ductility, without reducing its tensile strength by more than 10% by subjecting said object to a heat treatment at a temperature! /! ! 7.

I *! rature higher than its recrystallization temperature for a period sufficient to cause substantially complete recrystallization of the grains but insufficient to cause substantial grain growth, r 5 The preferred carbon content is up to about 0.1% by weight. the preferred nitrogen content is about 0.15 to 0.20% by weight. An alloy according to the present invention containing these amounts of carbon and nitrogen and in the indicated forging and partial annealing state is a preferred starting material * for surgical implants "for example hip stems and surgical nails. Such an alloy in this state has a unique combination of properties at room temperature i.e. a tensile strength of at least 105 x 10? Pa, ime resistance to the limit dr elasticity.

15 (less than 0 »2% deformation) of at least 6 300x 10 ^ Pa 'approximately an elongation (marks of 5.08 cm) of at least 18 5 °, a decrease in the surface (marks of 5 "08 cm) at least about 18%" excellent ductility "Rockwell hardness number of approximately 30 to 35" excellent resistance to corrosion by physiological fluids and excellent resistance to bending fatigue [none failure after 10 mil lions of alternating stress-tension stress cycles of at least 3,500 χ 1Pa and at least d *. 7 x 10 ^ Pa of maximum tension (ratio "A" of about 1)]. An alloy according to the present invention containing the preferred carbon and enasote contents and under cold rolling conditions is particularly suitable for the manufacture of plates for compression.

Careful maintenance of the amounts of chromium and molybdenum and especially of carbon and nitrogen within the critical limits revealed in this application is necessary in order to obtain the very good characteristics for the forging of the alloy. according to the invention. We do not realize these characteristics when the amounts of chromium 'molybdenum or? 35 of carbon are greater than 27.5 or 0.15% by weight, respectively, or when the amount of nitrogen is less than about 0.10% by weight or greater than about 0.25% by weight. It should be noted that the amounts of chromium and molybdenum are

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generally lower in this new alloy than in vitallium, but that one can nevertheless obtain practically superior properties by hot forging. The mechanism of the surprising interaction of the components of the alloy is not completely understood at present. Photo micrographs of the alloy according to the invention in the condition of forged and partially annealed objects reveal the existence of uniform fine grains with a uniform distribution of carbides. An austenitic structure is maintained in the matrix. We do not see significant amounts of nitride.

Iron and nickel are generally detrimental to corrosion resistance and should be kept as low as possible. On the other hand, manganese and silicon aid in the deoxidation of the molten mixture and improve the flowability and it is preferred that they be present in the alloy according to the invention at levels of about 0.4-4.0% by weight each. The alloy may also contain accidental impurities, for example sulfur or phosphorus, at levels so low that they do not significantly affect properties of the alloy.

The following examples are intended to further illustrate the invention without limiting it.

EXAMPLES 1-3

6 to 35 mm thick cast bars having the following composition are annealed with dissolving for one hour under an argon atmosphere at a temperature of 1228 ° and under a pressure of 100 to 150 microns of mercury:

Percentages by weight Chromium 26.80 30 Molybdenum 5.20

0.235 nitrogen

Carbon 0.059

Manganese 0.52

Silicon 0.58 35 Iron. Oj43

Nickel 0.27

Cobalt stays

They are quenched by an asote current, they are forged 9.

»At 1145 ° C in a forging press i they are heat treated to recrystallize the grains for 20 minutes at 1149 ° C, they are forged again at 1149 ° C to a thickness of 4j37 mm and then they are molded in the conditions of forging at a thickness of 3.175 mm

Some of the bars are then heat treated to recrystallize the grains (partial annealing) in the air for one hour at 1093 ° C (Example 1), some others are heat treated to recrystallize the grains (partial annealing) in the air for one hour at 112 ° C. (example 2) and certain others are left as forged (example 3). The following results are obtained concerning the mechanical properties.

Example Resistance Limit dallas- Allon- Limit of resistance to number; . tensile fatigue strength (0.2% deformation-% by bending (a) (Pa) mation, Pa) Voltage Maximum alternating voltage _____ (Pa) (bj (Pa) (b) 1 12 655x105 7 171xl05 23 3 5S5xlOb 7 311xl05 2o 2 12 655x105 7 171xl05 30 3 13 077x105 11 249xl05 6 3 832xl05 7 874xl05 7 (a) no break after 10 cycles __ (b) "A" ratio of 0.95 NOTE. - We define the ratio " A ”as the amplitude of the tension divided by the mean tensile tension.

The average tensile tension is the algebraic sum of the maximum and minimum tensions in the cycle. EXAMPLE 4

The alloy components are melted by an air induction melting technique and an ingot 6.88 cm in diameter and 70.11 cm in length is poured. Nitrogen is added to the molten mixture as chromium nitride. The ingot is used as an electrode for remelting electro-metallurgical slag into an ingot of 10.16 cm in dia-.35 meter and 38.10 cm in length having the following composition:

Weight percent Chrome 25.80

Molybdenum 5.49 /. - ~ s.

/ 10.

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Nitrogen Ojl26

Carbon 0.06

Manganese 0.57.

Silicon 0.49 5 Iron 0.50

Nickel 0.43

Cobalt stays

This ingot is annealed with solution for 3 hours at 1176 ° C. and it is then forged at 1149 ° C. in a square bar of 63.5. One part of this square bar forged at 1149 ° C. is hot rolled. into a 0.635 cm thick plate and the other part is hot rolled at around 1149 ° C. into a 2.54 cm diameter round bar. The 0.635 cm thick plate is then reduced when cold to a 0.476 cm thick plate.

Part of the 2.54 cm diameter bar is used as a raw material for hot forging hip rods. The remainder is reduced hot to a rod of 0.635 cm in diameter, then cold to a rod of 0.476 cm in diameter. A part of this ring, 0.476 cm in diameter, is used to forge a screw blank by hot pressing.

The tensile properties of the 0.476 cm plate and a portion of the 0.476 cm diameter rod are studied at room temperature. 25 Sample Limit stress Limit stress Extension- in tension (? A) of elasticity (0.2% »% __ · __ of deformation, Pa) __

0.476 cm thick plate 30 cm 18 420xl0ü 15 889 x 10 6.4

Rod of 0.476 cm in diameter18 445x10? EXAMPLE 5 '35 In a manner analogous to that described in example 4, an ingot of 10.16 cm in diameter and 38.10 cm in length is produced, having the following composition:

Percentages by weight Chromium 26.93 40 Molybdenum 5.13 11.

0.205 nitrogen

Carbon 0.07

Manganese 0.70

Silicon 0.52.5 Iron 0.17

Nickel 0.10 'Cobalt remains

This ingot is annealed with solution p ·· * fani 3 hours at 1176 ° C and then forged at 1149 ° C in a b'a :: '- ~ 2 <L0 square of 6.35 cm. One part of this square "" = b-ar.'e forged at 1149 ° C is hot rolled into a 0.793 cm plate and the other part is hot and stamped at 1149 ° C in a round 2.54 cm in diameter. Then reduce the plate 0.73 cm thick when cold to a 0.635 cm thick plate> * 15 Part of the bar is 2.54 cm · Diameter as raw material for hot forging '"hip rods. We reduce the rest to a rod of '* *' 53 cm by working it hot, then working it to d into a rod of 0.635 cm in diameter.

The tensile properties at room temperature of the 0.635 cm thick plate and the 0.635 cm diameter plate are studied.

Elastic Limit Resistance Sample ~ Elongated1 tensile strength. (0.2% of% 25 _ __ (Pa) _ deformation, Pa) - -----

0.476 e c- cm thick plate 13 780x10 11 670x10 12

Rod, 0.476 cm in diameter, 30 meters 14 975x10 12 092x10 19 EXAMPLE 6 *. . x t \

Manufacture of implants for prostheses chirurr: .- "-It can transform a cast ingot of form '' * ~~ matic having the following composition:’ 35 Percentages by weight

Chrome 22 to 27 'Molybdenum 3 to 6

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Nitrogen 0.10 to 0.25 (from pr '' c 0.15 to '^ 40 Carbon Up to about 0.15 (from pr_ to about 0.12, b

Manganese Up to 1 to about 1

Silicon Up to about 1

Iron Up to about 2

Nickel Up to approximately 2 t 5 Cobalt remains in a prosthesis implant as follows.

This ingot is passed through one or more cycles of hot working alternately at approximately 1093 ° C and annealing with dissolution (for approximately 1 hour by 2.5 * 10 cm thickness at approximately 1176 ° C in the air or in a partial vacuum). The alloy is hot worked at around 1093 ° C one last time in a cylindrical bar of about 2.54 cm in diameter and then hot forged at around 1120 to 1149 ° C in a hip rod or in another desired shape. The alloy object is then partially annealed by heat treatment in air or in a partial vacuum for about an hour at about 1068 ° C to 1093 ° C (grain recrystallization) and then it is worked in the machine and polish it into a final prosthesis implant.

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Claims (13)

13. "* 1. - Fabricated alloy" characterized in that it consists essentially of approximately 22 to 27% by weight of chromium "approximately 3 to 6% by weight of molybdenum" approximately 0.10, 5 to 0, 25% by weight of nitrogen, up to about 0.15% by weight of carbon, up to about 1% by weight of manganese, up to about 1% by weight of silicon, up to about 2% by weight of iron, up to about 2% by weight of nickel and the rest of cobalt. * 10 2. - Alloy according to claim 1, characterized in that it contains 0.15 to 0.20% nitrogen. O w 3. Alloy according to claim 1 / \ characterized in that it contains up to about 0.1% carbon. 4. Alloy according to claim 1, characterized in that it contains manganese and silicon in a percentage by weight of 0.4 to 0.6 each. 5. Object, characterized in that it is manufactured in the alloy according to claim 1. 6. Surgical implant, characterized in that it is manufactured in the alloy according to claim 1. 7. Object in hot forged alloy, characterized - by the fact that it consists essentially of approximately 22 to 27% by weight of chromium, approximately 3 to 6% of molybdenum, approximately 0.10 to 0.25% by weight nitrogen, up to about 0.15% by weight of carbon, up to about 1% by weight of manga nese, up to about 1% by weight of silicon, up to about 2% by weight of iron, up to about 2% by weight of nickel, and lice the rest of cobalt. 8. Object according to claim 7, characterized r 30 in that it contains 0.15 to 0.20% nitrogen. 9. Object according to claim 7 or 8, characterized in that it contains up to about 0.1% by weight of carbon. 10. Object according to claim 7, characterized in that it contains manganese and silicon in a proportion of 0.4 to 0.6% by weight each. 11. Object according to claim 7, characterized in that the object is in the forged state. / Λ 14. ( 12. Object according to claim 7, characterized in that the object is in the forged state and partially annealed. 13. Object according to claim 7 or 12, charac- * terized in that the object is a surgical implant. 14. A surgical implant according to claim 13, characterized in that it is in the form of a hip prosthesis rod. T é